The present invention relates to an image recording apparatus for recording images using photosensitive pressure-sensitive materials, and more particularly to an image recording apparatus in which a latent image is formed on a photosensitive pressure-sensitive image recording material by exposure, and the image recording material is pressed against an image receiving material for development of the image.
An example of a conventional image recording apparatus using microcapsules containing a photosensitive image recording material employs synthetic macromolecular resin wall capsules containing a vinyl compound, photopolymerization initiator and coloring agent precursor. Such an apparatus is disclosed in commonly assigned Japanese Unexamined Published Patent Application No. 179836/1982. In this apparatus, the microcapsules are hardened in the pattern of an image by optical exposure and then pressurized so that microcapsules which were not hardened are broken to discharge the coloring agent precursor thereby to form a color image. This apparatus is advantageous in that an image of high picture quality can be readily obtained by dry processing.
However, the above-described photosensitive material is disadvantageous in that it has a much lower photosensitivity than a photosensitive material using silver halogenides such as common photographic emulsions.
This difficulty has been eliminated by the provision of a novel photosensitive material, as described, for example, in commonly assigned Japanese Unexamined Published Patent Application No. 275742/1986. This novel photosensitive material is high in photosensitivity and provides an image high in picture quality using simple dry processing. The photosensitive material is formed by coating a support at least with photosensitive silver halogenide, a reducing agent, a polymerizing compound and a color image forming material. Of these materials, at least the polymerizing compound and the color image forming material are, in combination, sealed in microcapsules.
An image recording apparatus using the above-described photosensitive material is disclosed in Japanese Unexamined Patent Publication No. 147,461/1987. In that apparatus, first the image recording material is optically exposed to form a latent image thereon, and then subjected to thermal developing so that, in the region of the image, the polymerizing compound is polymerized to produce macromolecular compound to thereby harden the microcapsules. Thereafter, the image recording material thus processed is stacked on an image receiving material having an image receiving layer onto which the color image forming material can be transferred, and the image recording material and the image receiving material are pressurized so that, in the region where no latent image is formed, some of the microcapsules are broken to transfer the color image forming material to the image receiving material to form a visible image.
In the image recording apparatus, the photosensitive material and the image receiving material are stacked together and are then pressurized by a pair of pressurizing rollers so that the color image forming material is accurately transferred to the image receiving material. For this purpose, the pressurizing rollers must be sufficiently long that they cover the width of the photosensitive material and the image receiving material. Therefore, when one of the pressurizing rollers is pressed at both ends against the other, for instance by springs, the one pressurizing roller is bent so that only the two end portions of the latter are pressed against the other pressurizing roller. That is, pressure is not sufficiently applied to the middle portion of the photosensitive material, and accordingly the color image forming material is not accurately transferred to the image receiving material.
To eliminate the above-described difficulty, an image recording apparatus has been proposed in which a back-up roller whose middle portion is larger in diameter than the remaining two end portions is used to press only the middle portion of one of the pressurizing rollers against the other so that the above-described bending of the pressurizing roller is corrected. However, the image recording apparatus is still disadvantageous in that, since the large-diameter middle portion of the back-up roller tends to bend in the longitudinal direction, only the two end portions of the large-diameter middle portion press against the pressurizing roller, as a result of which the pressure applied by the pressurizing roller is still not uniform, and hence the color image forming material is still not accurately transferred to the image receiving material.
Moreover, if the pressure distribution of the pressurizing rollers is not uniform as described above, the photosensitive material and the image receiving material have a tendency to be partially displaced towards the part or parts of the pressurizing rollers where the pressure is lower, as a result of which the photosensitive material and the image receiving material are creased. The amount of creasing increases with the amount of nonuniformity of the pressure distribution. As a result, the color image forming material is not accurately transferred to the image receiving material, and the resultant image is considerably irregular in density.
Also, if the pressurizing rollers' pressure distribution is not uniform as described above, the photosensitive material and the image receiving material, being held by the pressurizing rollers, have a tendency to be creased. Due to the creases, the nonuniformity of the pressure distribution is further increased, and the unevenness in density of the image becomes more significant.
Furthermore, not only in the above-described image recording apparatus, but also in some electrophotographing apparatuses, the nip rollers are used to apply a high pressure to the image recording material to obtain the image. In this operation, it is unavoidable that the image recording material is nonuniformly pressurized.
To eliminate the above-described difficulty, a skew roll pressurizing device has been proposed in which a pair of pressurizing nip rollers are arranged in such a manner that their axes form a slight angle so that the pressure provided in the nip region of the two rollers is uniform over their entire length. For the same purpose, a back-up roller pressurizing device has been proposed in which two back-up rollers are arranged outside a pair of pressurizing nip rollers so that the pressure provided in the nip region of the pressurizing nip rollers is uniform over the entire length.
However, the former device is disadvantageous in that the device cannot handle a plurality of image recording materials differing in thickness or in width. On the other hand, when the image recording material and the image receiving material stacked together are conveyed while being pressurized by the pressurizing nip rollers, the image recording material and the image receiving material are conveyed in directions perpendicular to the axes of the respective nip rollers they contact, and therefore the rear end portion of each of the image recording material and image receiving material tends to be greatly shifted from the front end portion in the widthwise direction.
The latter device is also disadvantageous in that, since it requires two back-up rollers in addition to the pressurizing nip rollers, the device is unavoidably bulky and high in weight.
Furthermore, these two devices suffer from a difficulty that they are intricate in construction because it is necessary to adjust the pressurizing forces of the pressurizing nip rollers.